Steroidal nuclear receptor (NR) ligands are known to play important roles in the health of both men and women. Testosterone (T) and dihydrotestosterone (DHT) are endogenous steroidal ligands for the androgen receptor (AR) that appear to play a role in every tissue type found in the mammalian body. During the development of the fetus, androgens play a role in sexual differentiation and development of male sexual organs.
Further sexual development is mediated by androgens during puberty. Androgens play diverse roles in the adult, including stimulation and maintenance of male sexual accessory organs and maintenance of the musculoskeletal system. Cognitive function, sexuality, aggression, and mood are some of the behavioral aspects mediated by androgens. Androgens have a physiologic effect on the skin, bone, and skeletal muscle, as well as blood, lipids, and blood cells (Chang, C. and Whipple, G. Androgens and Androgen Receptors. Kluwer Academic Publishers: Boston, Mass., 2002)
Many clinical studies with testosterone have demonstrated significant gains in muscle mass and function along with decreases in visceral fat. See, for example, Bhasin (2003) S. J. Gerontol. A Biol. Sci. Med. Sci. 58:1002-8, and Ferrando, A. A. et al. (2002) Am. J. Phys. Endo. Met. 282: E601-E607. Androgen replacement therapy (ART) in men improves body composition parameters such as muscle mass, strength, and bone mineral density (see, for example, Asthana, S. et al. (2004) J. Ger., Series A: Biol. Sci. Med. Sci. 59: 461-465). There is also evidence of improvement in less tangible parameters such as libido and mood. Andrologists and other specialists are increasingly using androgens for the treatment of the symptoms of androgen deficiency. ART, using T and its congeners, is available in transdermal, injectable, and oral dosage forms. All current treatment options have contraindications (e.g., prostate cancer) and side-effects, such as increased hematocrit, liver toxicity, and sleep apnoea. Side-effects from androgen therapy in women include: acne, hirsutism, and lowering of high-density lipoprotein (HDL) cholesterol levels, a notable side-effect also seen in men.
Agents that could selectively afford the benefits of androgens and greatly reduce the side-effect profile would be of great therapeutic value. Interestingly, certain NR ligands are known to exert their action in a tissue selective manner (see, for example, Smith et al. (2004) Endoc. Rev. 2545-71). This selectivity stems from the particular ability of these ligands to function as agonists in some tissues, while having no effect or even an antagonist effect in other tissues. The term “selective receptor modulator” (SRM) has been given to these molecules. A synthetic compound that binds to an intracellular receptor and mimics the effects of the native hormone is referred to as an agonist. A compound that inhibits the effect of the native hormone is called an antagonist. The term “modulators” refers to compounds that have a spectrum of activities ranging from full agonism to partial agonism to full antagonism.
SARMs (selective androgen receptor modulators) represent an emerging class of small molecule pharmacotherapeutics that have the potential to afford the important benefits of androgen therapy without the undesired side-effects. Many SARMs with demonstrated tissue-selective effects are currently in the early stages of development See, for example, Mohler, M. L. et al. (2009) J. Med. Chem. 52(12): 3597-617. One notable SARM molecule, Ostarine™, has recently completed phase I and II clinical studies. See, for example, Zilbermint, M. F. and Dobs, A. S. (2009) Future Oncology 5(8):1211-20. Ostarine™ appears to increase total lean body mass and enhance functional performance. Because of their highly-selective anabolic properties and demonstrated androgenic-sparing activities, SARMs should be useful for the prevention and/or treatment of many diseases in both men and women, including, but not limited to sarcopenia, cachexias (including those associated with cancer, heart failure, chronic obstructive pulmonary disease (COPD), and end stage renal disease (ESRD), urinary incontinence, osteoporosis, frailty, dry eye and other conditions associated with aging or androgen deficiency. See, for example, Ho et al. (2004) Curr Opin Obstet Gynecol. 16:405-9; Albaaj et al. (2006) Postgrad Med J 82:693-6; Caminti et al. (2009) J Am Coll Cardiol. 54(10):919-27; Iellamo et al. (2010) J Am Coll Cardiol. 56(16):1310-6; Svartberg (2010) Curr Opin Endocrinol Diabetes Obes. 17(3):257-61, and Mammadov et al. (2011) Int Urol Nephrol 43:1003-8. SARMS also show promise for use in promoting muscle regeneration and repair (see, for example, Serra et al. (Epub 2012 Apr. 12) doi:10.1093/Gerona/gls083), in the areas of hormonal male contraception and benign prostatic hyperplasia (BPH), and in wound healing (see, for example, Demling (2009) ePlasty 9:e9).
Preclinical studies and emerging clinical data demonstrate the therapeutic potential of SARMs to address the unmet medical needs of many patients. The demonstrated advantages of this class of compounds in comparison with steroidal androgens (e.g., tissue-selective activity, oral administration, AR selectivity, and lack of androgenic effect) position SARMs for a bright future of therapeutic applications. Accordingly, there remains a need in the art for new SARMs for therapeutic use.